1. Field of the Invention
The present invention relates to a color cathode ray tube (CRT), and more particularly, to a color CRT in which a band force of a reinforcing band is set with an optimum condition for an explosion proof of the color CRT.
2. Description of the Related Art
Generally, a color CRT is a device for displaying images, and is divided into a curved surface CRT and a flat CRT according to an outer shape of a panel.
The curved CRT having an outer surface of a curved surface has several problems such as a screen distortion, eyes fatigue due to a light reflection, and etc. thereby to have decreased demands. On the contrary, the flat CRT having an outer surface of a plane has many advantages that a screen is not distorted, reflection by external light is minimized, and a visual region is maximized, so that demands for the flat CRT are being increased gradually.
FIG. 1 is a longitudinal section view showing a color CRT in accordance with the related art, FIG. 2 is a section view showing a single reinforcing band, and FIG. 3 is a section view showing an overlapped reinforcing band.
As shown, the size color CRT 10 comprises: a panel 1 having an effective surface on which a phosphor 1a is deposited; a mask 2 for performing a color selection for an electron beam made to be incident on the inner side of the panel 1; a funnel 3 coupled to a rear surface of the panel 1 for maintaining a vacuum state inside the CRT; a deflection yoke 5 for deflecting an electron beam emitted from an electron gun 4; and a reinforcing band 6 coupled to a skirt portion 1b of the panel 1.
In the related color CRT, when an image signal is inputted to the electron gun 4, the electron gun 4 emits an electron beam and the emitted electron beam is accelerated and focused towards the phosphor 1a of the panel 1 by a voltage applied from each electrode.
At this time, the electron beam is deflected by the deflection yoke 5 and then passes through slots formed at the mask 2 thereby to perform a color selection. Then, the electron beam collides with the phosphor 1a of the inner surface of the panel 1 thus to make each phosphor emit light, thereby displaying images.
At this time, since the color CRT maintains a vacuum state by the panel and the funnel, a compression stress or a tension stress is applied to the inside and outside of the CRT.
Since glass generally has a weak characteristic against the tension stress than the compression stress, a side portion of the panel becomes structurally weak than other portions.
Also, when a little external impact is applied in a state that the compression stress and the tension stress are applied to the CRT of a vacuum state, an explosion phenomenon that the panel or the funnel are exploded is generated. The explosion phenomenon makes the CRT not be operated and causes danger to the user's safety. To prevent this, a reinforcing band 6 is coupled to the skirt portion 1b of the panel 1. The reinforcing band 6 is positioned to cover a mold match line M which is naturally formed at the time of forming the panel. The reinforcing band 6 shown in FIG. 2 is a single type, and the reinforcing band 6 shown in FIG. 3 is an overlapped type.
Generally, a band force F of the reinforcing band can be expressed as a following condition, F=yield strength*thickness of reinforcing band*width of reinforcing band. Herein, since the yield strength is generally determined by a material of the reinforcing band, setting the thickness of the reinforcing band and the width of the reinforcing band is very important so as to set an optimum band force.
However, in the related color CRT, the band force of the reinforcing band applied to the panel was not set as an optimum state but was set to be too great or less.
When the set band force is too less than an optimum band force, a stress of the panel is not sufficiently released thus to have a difficulty in obtaining the safety. On the contrary, when the set band force is too greater than the optimum band force, a fabrication cost of the reinforcing band is increased even if the safety can be obtained.
According to this, an optimum setting of the band force which minimizes the fabrication cost of the reinforcing band and obtains the safety for the explosion is absolutely required.